1. Field of the Invention
The present invention relates to an apparatus and method for TTR offset control in ADSL, more particularly, which can control TTR offset in order to remove NEXT or FEXT noise that would otherwise take place in services due to matching between ADSL and TCM-ISDN. The present invention relates to a method and a system of detecting a duplicate service set identifier (SSID) via self-scanning in a wireless local area network (WLAN).
2. Description of the Related Art
Generally, in an 802.11 WLAN infrastructure mode, an access point (AP) establishes a network using an SSID, which is the same as that of a client, in order to provide a data service to the client.
Accordingly, the client can access the AP via the SSID of the network, to which it attempts to connect, in order to be provided with a suitable data service. That is, as described in the following paragraphs, the client transmits a probe request packet and then waits for a probe response packet in order to access an AP or to scan neighbor APs.
FIG. 1 is a view illustrating a general example of a probe request packet and a probe response packet. If the SSID field of the probe request packet, received from a client, is the same as that of the SSID of an AP or is a broadcast SSID, the AP transmits a probe response packet to the client by adding its own SSID to an SSID field of the probe response packet. Accordingly, in order to scan neighbor APs, the client transmits a probe request packet to the neighbor APs by adding a broadcast SSID thereto, and then collects AP information of a corresponding channel by referring to the SSID fields of probe response packets, received from the neighbor APs. This process is referred to as active scanning scheme.
On the contrary, the client can receive beacons, which are periodically transmitted from the neighbor APs, to collect AP information of a corresponding channel by referring to the SSID in the beacons. This process is referred to as passive scanning scheme.
WLAN users generally purchase APs, which are widely distributed in the market. However, in the case that a user attempts to use a purchased AP without changing the SSID setting thereof, the SSID of the purchased AP may be the same as that of a neighbor AP. If a neighbor AP present within a service set is accidentally using the same SSID, the client would be confused to identify an AP, to which it attempts to connect. Hence, abnormal data services can be caused. That is, the client may access an incorrect AP, and thus a data service may fail due to authentication failure. The client may repeat connection between two APs having the same SSID, thereby risking the stability of the service. It is also possible that another client accesses the user AP to be freely provided with a data service.
A specific client can identify whether or not the same SSID is present by collecting neighbor AP information via active scanning or passive scanning. However, in the case of an AP having a hidden SSID, its beacon does not include SSID information. This type of AP also does not respond to a probe request, which uses a broadcast SSID.
When the client terminal scans the neighbor APs via a conventional scanning scheme, it is impossible to detect an AP having a hidden SSID. Therefore, the problem is that the presence of an AP, which has the same SSID as the user AP, cannot be identified.